In modern surgery, an important instrument available to medical personnel is the powered surgical tool. Often, this tool is a handpiece in which a motor is housed. Secured to the handpiece is a cutting accessory designed for application to a surgical site on a patient in order to accomplish a specific medical task. Some powered surgical handpieces are provided with drills or reamers for cutting bores or other void spaces in tissue. The ability to use powered surgical tools on a patient lessens the physical strain of surgeons and other medical personnel when performing procedures on a patient. Moreover, most surgical procedures can be performed more quickly, and more accurately, with powered surgical tools than with the manual equivalents that preceded them.
One such type of tool is the surgical rotary handpiece. A rotary handpiece has spindle that rotates in response to actuation of the handpiece motor. Attached to the front end of the spindle is a coupling assembly. The coupling assembly releasably holds a device to the spindle so that the device rotates in unison with the spindle. Generally, two types of devices are releasably coupled to a handpiece spindle. One type of device is the actual cutting accessory, for example, the drill or the reamer. The cutting accessory has a shaft. The proximal end, the rear end, of the shaft is releasably held to the spindle by the coupling head.
The second type of device coupled to a rotary handpiece is a front end attachment. The attachment has a housing with opposed front and rear ends. An input shaft extends from the attachment rear end. The attachment front end has its own output spindle and complementary coupling assembly. Sometimes a gear assembly is located between the input shaft and the output spindle of an attachment. The gear assembly contains gears that typically increase the torque/decrease the speed of the rotational motion applied to the attached cutting accessory through the attachment output spindle. When the attachment is attached to the handpiece, the attachment housing is often statically coupled to the handpiece housing. The handpiece coupling assembly holds the attachment input shaft to the handpiece spindle. The actual cutting accessory is locked to the attachment spindle. The attachment speed reduces or speed increases the rotational moment output by the handpiece that is applied to the cutting accessory. Typically an attachment is used to speed reduce/torque increase the rotational moment of the attached cutting accessory.
Other attachments provide a means to attaching a cutting accessory to the handpiece spindle so the two components rotate at the same speed. An attachment of this variety typically does not have a gear assembly.
It is known to provide surgical handpieces with internal torque increasing/speed reducing gear assemblies. Some of these assemblies have plural output heads. This gear assembly receives the rotational moment from the motor output shaft and simultaneously rotates the plural output heads at different speeds. A clutch selectively connects the drill output spindle for rotation to one of the gear assembly output heads. The output speed/torque producing capability of the handpiece spindle is set by setting the clutch to selectively set the gear assembly-to-drill spindle connection. In some circumstances, these assemblies eliminate the need to employ a front head torque increasing/speed reducing attachment.
Known handpiece gear and clutch assemblies are relatively long in length. A disadvantage of this type of structure is that it increases the overall length of the handpiece. This runs contrary to a goal of efficient handpiece design, namely, the handpiece should be made as short as possible. This is because it easier for a surgeon to accurately position the working end of the cutting accessory that is relatively close to his/her hand than one further away. To provide this feature it is, therefore, desirable to construct a handpiece that has an overall length, especially from the motor forward, that is as compact as possible.
Moreover, a surgical handpiece is typically designed to be held at or near its center of gravity. This design reduces the physical stress to which the surgeon is exposed when he/she holds and needs to precisely position the tool in order to accomplish a given surgical procedure. The positioning of any mass away from a surgical handpiece's center of gravity/hand hold makes it more difficult for the surgeon to hold and precisely position the handpiece. Known gear and clutch assemblies, because of their lengths and masses, are typically off center from the center of gravity of the handpieces with which they are integral. During a surgical procedure, it may be necessary for the surgeon to precisely control a tool's position for an extended period. The off-center mass of a gear and clutch assembly can add to the physical stress to which the surgeon is exposed when so holding the tool.
Other disadvantages are associated with known coupling assemblies used to releasably hold cutting accessories and attachments to the handpiece spindles. Known coupling assemblies are effective for transmitting torque, rotational moment, from a handpiece spindle to the attached accessory/attachment and hold the accessory/attachment firmly to the spindle. Nevertheless, many coupling assemblies allow that shaft of the attached accessory/attachment to radially shift position, relative to the axis of the associated handpiece spindle.
The looseness of this fit allows the accessory/attachment to wobble when coupled to the handpiece. Wobble present in the shaft adjacent the surgical handpiece is amplified at the distal free end of the attachment, the end applied to the surgical site. Some attachments, for example reamers and drills used to perform certain procedures have lengths of 10 cm or more. The wobble, the radial shifting, at the distal end of these attachments can therefore be quite significant. The presence of this movement can appreciably add to the overall control the surgeon must exert in order to ensure that the working end of the attachment remains accurately position at the surgical site to which the attachment is applied.